In the processing of radar video signals by filtering, a residue of the filtering operation may sometimes be sufficiently large so as to falsely indicate the presence of a target when, in fact, the residue resulted from a strong clutter signal. For example, in an MTI (moving target indication) radar, the filter or canceller typically comprises delay lines having delays in integral multiples of the transmission period (the reciprocal of the pulse repetition frequency). The subtraction of a strong echo such as that produced by a water tower from the previously occurring echo of the same water tower produces a cancellation of the water tower echo signal except for the residue of the filtering operation. A target such as a moving aircraft moving toward or away from the radar results in an echo signal which is not canceled, the moving target echo signal being passed without attenuation by the filter due to the changing range and echo propagation time as is known from the theory of MTI radars. The theory of MTI radars is explained in the book "Radar handbook" by M. I. Skolnik, published by McGraw-Hill Book Company in 1970.
A problem arises in that previous attempts of the prior art to reduce the overloading effect of large amplitude residue signals by decreasing the dynamic range of the IF (intermediate frequency) amplifier stages of the radar has produced MTI radars which do not achieve their maximum potential capability. An IF amplifier without the gain restriction produces, subsequent to the filtering or canceling operation, the aforementioned large residues from strong clutter with the attendant difficulties in obtaining data of the true target versus the clutter returns.